The invention relates to an electrode belt of a heart rate monitor, which belt is to be placed on the chest. A heart rate monitor is a device used in sports and medicine, the device measuring the human heart rate on the chest or at the wrist.
An electrode belt which belongs to a heart rate monitor and is to be placed on the chest is known to have such a structure that there is an electronics unit at the central portion of the belt and an electrode on both sides of the electronics unit. The electrodes measure the electric pulse of the heart and transmit the measurement result to the electronics unit via a conductor combining the electrode and the electronics unit. Components included in the electrode belt, such as the electronics unit and electrodes, are coated with plastic or rubber in order to protect the components from humidity, for instance. Depending on the structure of the electrode belt, the electronics unit often also comprises means for transmitting an electric pulse as an analogous burst to a receiver and display unit at the wrist, for example. Alternatively the electrode belt itself may contain means for storing and displaying the electric pulses.
Usually electrode belts have such a structure that a rubber or plastic supporting structure coating the components of the electrode belt is relatively rigid between the electronics unit and the electrodes. Such electrode belts are not very well suited for slim adults and children, since the electrode belt does not bend and adapt well enough to a body of a person with a narrow chest. In some of the prior art solutions, the problem has been approached such that the plastic supporting structure between the electronics unit and the electrode has an accordion-like shape, in which case the electrode belt can be bent immediately from outside the electronics unit. In the known solutions, the conductor combining the electronics unit and the electrode is a straight section inside the supporting structure having an accordion-like shape. The prior art solution is illustrated by FIG. 4B. It can be seen from the figure that a conductor 304 extends as a separate section along a supporting structure 300A/300B and pierces the supporting structure in point 412 illustrated by a broken line.
The prior art solution includes a serious weakness: when the accordion-like supporting structure is bent or stretched, there is a big risk of the conductor to be damaged or come loose from the electronics unit or the electrode.
The object of the invention is to implement an improved structure of an electrode belt. This is achieved by an electrode belt of a heart rate monitor, which is described in the following. It deals with an electrode belt of a heart rate monitor, the electrode belt comprising one or more electrodes for measuring the heart rate on the chest, an electronics unit for handling the information to be received from the electrode, a conductor for providing electrical contact between the electronics unit and the electrode, at least one wavelike supporting structure provided with alternating upwards and downwards directing sections and intended for protecting the conductor. The conductor protected by the supporting structure of the electrode belt follows the shape of the supporting structure, thus having a wavelike form.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention relates to an electrode belt of a heart rate monitor. In the specification of the invention, the electrode belt refers to a substantially belt-like structure, whereby the length of the belt to be wound around the chest is substantially greater than the width of the belt. Viewed from the side of the electrodes, the length of an electrode belt is typically 5 to 10 times greater than its width, although the invention is naturally not restricted to the fact how much bigger the length is compared to the width. According to a preferred embodiment, the electrode belt comprises means for transmitting heart rate information to a receiver unit to be held at the wrist, the receiver unit possibly also comprising display means for displaying the heart rate information. If the electrode belt comprises the means for transmitting the heart rate information to a receiver, such as a receiver at the wrist or an external computer, the electrode belt is called a transmitter electrode belt. The invention is not, however, restricted to the fact whether or not the electrode belt comprises transmitter electronics. The electrode belt itself may comprise memory means for storing heart rate information and/or display means for displaying the heart rate. However, the invention is not restricted to the fact whether the electrode belt itself comprises the memory means for storing heart rate information or whether the electrode belt comprises the display means for displaying the measured heart rate information. The invention is not restricted to the fact either, how many electrodes the electrode belt contains. According to a preferred embodiment, there are two electrodes, one on each side of the transmitter electronics, but also other solutions are possible. The invention is not restricted to the fact either, which material the coating, i.e. the supporting structure protecting the components of the electrode belt is made of. According to a preferred embodiment, the supporting structure is made of plastic, but it may also be made of rubber or a similar material that is easy to shape.
In accordance with the invention, the supporting structure between the electronics and the electrodes in the electrode belt of a heart rate monitor, which belt is to be placed on the chest, is made of an elastic material to provide the supporting structure with a flexible and wavelike shape with alternating upwards and downwards directing sections. The conductor which is to be found inside the supporting structure between the electrode and the electronics unit and which provides electrical contact follows the shape of the supporting structure and thus has a wavelike shape. In accordance with the invention, the conductor adapts to the wavelike shape of the supporting structure. According to a preferred embodiment, the conductor is placed into the middle of the supporting structure, which means that the distance from the conductor to a first surface of the supporting structure substantially equals to the distance from the conductor to a second surface of the supporting structure.
According to a preferred embodiment of the invention, the conductor inside the supporting structure is built onto a conduction base to support the conductor. The conductor made of an electrically conductive material can be built onto the conduction base by using known manufacturing methods, e.g. by pressing. The cross-section of the conductor is preferably round, but it can also have a strip-like or, when pressed onto a conduction base, a planar shape. The conduction base is formed from a flexible material, such as polyimide, polyethylene, polycarbonate or the like, preferably into a thin film. In the manufacturing stage at which an electrode belt is being molded, the conduction base is preferably formed to follow the wavelike shape of the supporting structure. According to a preferred embodiment, the conduction base of the electrode belt, functioning as a plate supporting the conductor, is a uniform piece, and thus both electrodes are connected to it and the conduction base extends through the electronics unit.
The wavelike shape of the supporting structure, conductor and conduction base according to the invention preferably means that this wavelike shape comprises at least one wave ridge and at least one wave trough. Preferably said wavelike shape is substantially a sine curve. According to a preferred embodiment, the shape becomes wavelike at the edge of the electronics unit, wherefore the belt can be bent immediately from the edge of the electronics unit. When the electrode belt is viewed from the side, i.e. from the level of the electrodes on the long side of the belt, the wavelike shape of the electrode belt can be seen. The supporting structure comprises a first surface on the side where the electrode of the electrode belt is, and a second surface on the opposite side of the first surface of the supporting structure, i.e. on the side that is to be placed away from the body. In a preferred embodiment, the wavelike shape of the electrode belt means that the distance between the first surface and the second surface of the supporting structure, measured perpendicularly from the first surface to the second surface, is substantially constant between two successive wave ridges of the wavelike shape of the supporting structure. The known solutions disclose that the wavelike shape only extends to one side of the belt, for example to the second surface of the supporting structure. Such a solution is for example an electrode belt disclosed in the publication U.S. Pat. No. 5,778,880, which comprises a stepwise slanting fastening strap 3 but a conductive plate 4 of which has a rigid structure. Thereby the stepwise shape is only to be found on the outer surface that is directed away from the body. No actual function is mentioned for the stepwise shape of the fastening strap in the publication; apparently it simply deals with a design feature.
The solution of the invention also differs from solutions in which the upper and lower surface of the supporting structures are wavelike, but the thickness of the supporting structure is not substantially constant. In other words, this section of the supporting structure is entirely pleated on its both sides in a wavelike manner. In the above solutions the conductor does not follow the shape of the supporting structure, but is substantially a straight section inside the supporting structure. In a preferred embodiment of the invention, the wavelike section between the electrode and the electronics unit is symmetrical so that when there is a ridge on the first surface of the supporting structure, there is a trough on the second surface. And vice versa, when there is a trough on the first surface, there is a ridge on the second surface. When the wavelike shape thus extends symmetrically on both surfaces of the supporting structure, the distance between two ridges on the first surface preferably equals to the distance between two troughs on the second surface, which correspond to said ridges.
The invention provides the advantage that the conductor following the shape of the supporting structure of the electrode belt is not at risk of stretching or coming loose from its ends when the electrode belt is bent or stretched.